Thyrotoxicosis is a hypermetabolic clinical syndrome caused by a pathological excess of circulating free T4 (thyroxine) and/or free T3 (tri-iodothyronine).
Although commonly done, thyrotoxicosis should not be confused nor synonymised with hyperthyroidism, the latter of which is a group of conditions characterized by abnormally elevated thyroid gland function (pathologically excessive production and secretion of thyroid hormones) that lead to thyrotoxicosis.
Signs and symptoms associated with thyrotoxicosis include 1:
- weight loss
- muscle weakness / tremor
- increased perspiration / heat intolerance
- palpitations / tachycardia or atrial arrhythmia / systolic hypertension
- stare and eyelid retraction (i.e. proptosis)
- reduced menstrual flow
In subclinical thyrotoxicosis (normal serum free T4 and T3 with low TSH), the patient may not have any symptoms.
The signs and symptoms attributed to thyrotoxicosis stem from the acceleration of normal physiological processes as a result of excessive serum concentrations of thyroid hormones.
There are multiple causes of thyrotoxicosis 1:
- excessive exogenous thyroid hormone iatrogenesis or ingestion (thyrotoxicosis factitia)
- thyroiditis (where there is excessive release of stored thyroid hormone without a concomitant increase in synthesis)
- high-dose radiation therapy
- surgical manipulation
- iodinated contrast administration (see: contrast medium-induced thyrotoxicosis)
Treatment and prognosis
Upon a precipitating event, “uncomplicated” thyrotoxicosis will transform into a thyrotoxic crisis (thyroid storm) if left unmanaged.
- thyroid inflammatory disease
- thyroid neoplasms
- thyroid nodules
- assessment of thyroid lesions
- postoperative assessment after thyroid cancer surgery
- ultrasound-guided fine needle aspiration of the thyroid